This invention relates generally to coal pulverizer seals. More particularly, the present invention relates to mill-housing penetration seals for ring-bowl coal pulverizing mills. Ring-bowl mills are used in coal-fired furnaces because pulverized coal burns substantially like gas and, therefore, fires are easily lighted and controlled. Pulverized coal furnaces can be readily adapted to burn all coal ranks from anthracite to lignite.
When in operation, raw coal enters the pulverizer through a center feed pipe onto a rotating bowl. Centrifugal force causes the coal to move outward from the center and under journal assemblies, where it is crushed by large rolls. The partially pulverized material passes over the rim of the bowl, where the coal is entrained by the rising hot-air stream and pyrites and tramp iron that enter the mill with the coal fall into the millside. The rejected materials are swept out of the mill into an external hopper. The air-transported partially pulverized coal is classified on the basis of size, with the larger, heavier particles being returned to the bowl and coal having the desired particle size exiting the pulverizer.
The rotating bowl is driven by a gear drive disposed below and external to the mill housing. Since the gear unit does not penetrate the mill housing, it is not directly exposed to the pulverized coal entrained in the primary air. A mill-housing penetration seal on the grinding-bowl support hub, above the gear unit prevents airborne coal particles from settling into the gear unit. Conventionally, the mill-housing penetration seal has comprised upper and lower labyrinth seals. However, such labyrinth seals have been difficult to adjust to maintain the tight tolerances required to prevent introduction of coal particles into the gear unit.
Briefly stated, the invention in a preferred form is a brush seal assembly for a coal pulverizer which includes multiple identical assembly segments. Each assembly segment comprises an arcuate brush assembly which includes a brush and an adjusting segment. A radially inner end of the brush contacts the yoke which transmits rotary motion from the motor to the pulverizer bowl. The radially outer end is connected to the adjusting segment. At least one elliptical opening extending longitudinally through the adjusting segment, each elliptical opening extends radially from an inner end to an outer end. The assembly segment also comprises at least one clamping block assembly. Each clamping block assembly includes a clamping block and an adjustable bearing device. A substantially circular opening extends longitudinally through the clamping block. The bearing device has a first portion connected to the clamping block, a second portion which is radially moveably mounted on the first portion, and a lock for locking the second portion at a selected radial position. The second portion is engaged to the adjusting segment of the brush assembly for biasing the brush assembly in the radial direction. The assembly segment further comprises at least one mounting bolt. Each mounting bolt has a threaded shaft extending longitudinally upward from the head, through the circular opening of the clamping block assembly and the elliptical opening of the adjusting segment, to a distal end portion which engages an opening of the seal housing to clamp the brush assembly and the clamping block assembly to the seal housing.
The brush assembly preferably comprises an arcuate brush segment which includes the brush and a brush holder. The brush holder has a radially outer mounting plate portion and a radially inner brush receptacle portion, with the radially outer end of the brush being mounted in the brush receptacle portion. The brush assembly also comprises an arcuate adjusting segment which includes a radially extending mounting portion and an longitudinally extending bearing portion. The mounting portion of the adjusting segment is mounted to the mounting plate portion of the brush segment. The first portion of each adjustable bearing device is a threaded rod and the second portion and lock of each adjustable bearing device are a pair of jam nuts. The threaded rod extends radially from an inner end mounted to the clamping block, through the first jam nut, a circular hole in the bearing portion of the adjusting segment, and the second jam nut.
The brush seal assembly may also comprise an arcuate brush guard segment including a mounting portion which is clamped between the brush assembly and the seal housing. An extension portion of the brush guard segment extends radially inward over a portion of the brush to a radially inner end spaced a distance from the yoke. Preferably, the brush guard segment is composed of a material which is softer than the material of the yoke.
It is an object of the invention to provide a seal which is more tolerant to runout and field conditions than conventional coal pulverizer seals.
Other objects and advantages of the invention will become apparent from the drawings and specification.